Depends because if that roof is no more than old than 10 years or more that roof could still be removed layer by layer , I have encounter with really old roofs and I'm talking about really old roofs and the degree of the life span of a shingle is pretty tuff to discuss, because we take in matter...
It's just like Jenga bro , to much weight and the Building will go down . Not necessarily the existing roof will need support, il suggest giving a look at the points were the roof is hanging on and by your perspective youl see if that roof will need a additional support, sometimes even just...